Sparkly, if an engagement ring is a sign of marriage, what’s a wedding ring?
I forgot to mention that despite the diamond cartel’s slogan “Diamonds are forever,” they’re not. My mother’s diamond got shattered internally when something fell on it. After that, it was basically worthless.
Akuperma, as you probably know, the difficulty of appraising diamonds (or any stone) is the reason that halacha doesn’t allow them for kiddushin.